Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.88	13.133%	$254.4135	$254.41	$254.40	$254.40
Purchase #2	$87.60	13.682%	$99.5854	$99.59	$99.60	$99.60
Purchase #3	$244.30	4.663%	$255.6917	$255.69	$255.70	$255.70
Purchase #4	$182.54	13.681%	$207.5133	$207.51	$207.50	$207.50
Purchase #5	$140.51	3.125%	$144.9009	$144.90	$144.90	$144.90
Purchase #6	$174.32	10.380%	$192.4144	$192.41	$192.40	$192.40
Purchase #7	$241.56	7.266%	$259.1117	$259.11	$259.10	$259.10
7 purchase totals =	$1,295.71		$1,413.6309	$1,413.62	$1,413.60	$1,413.60